AAtrox jungle bug

Hello ,i found an aatrox's bug so when im jungling with aatrox, first,i smited the stoner,so i have the buff the problem is ,when i stack 5 hit on stoner (so the 6th hit is stun) but after that,stoner was dead,so i come to the red monster if the next (6th ) hit is normal hit,the red monster wont get stunned (wasting my 5 stack stun), => this is bug if the next (6th) hit is steal blood hit (passive W) ,the red monster get stunned => this is normal i main aatrox so this bug is a big problem for me,solve it asap thanks